Synthesis And Electrorheological Properties Of Hierarchical Structured Nanocomposite Particles

Electrorheological Fluids（ERF） composed of dielectric particles dispersed in a nonconducting or weakly conducting liquid, undergo dramatic, reversible changes when apply to an external electric field. Apparent suspension viscosities and shear stress can increase several orders of magnitude. The electro-rheological fluid（ERF） is one kind of controllable suspension with micron-sized particles dispersed in a carrier medium. In the absence of external electric, ERF presents a Newtonian behavior. Then it can abruptly transforms into high viscosity plastic-like solid from low viscosity fluid within milliseconds under an applied electric field. The Chromium ion doped Bi Fe O3 nanoparticles, flower like Fe2O3/PANI hierarchical structure particles, anisotropic Ti O2/PANI hierarchical structure particles and PANI/PPy ring-like nanofibers are synthesized by different approach and characterized by the means of X-ray Powder Diffraction（XRD）, Scanning Electron Microscopy（SEM）, Transmission Electron Microscopy（TEM）, et al.. The main contents and major results are given as follows:（1）A series of Cr-doped multiferroelectric Bi Fe O3 nanoparticles were synthesized via a facile sol gel method. The resultant Cr-doped Bi Fe O3 was characterized by means of different techniques, such as scanningelectron microscopy（SEM）, energy-dispersive spectroscopy（EDS）, transmission electron microscopy（TEM）, X-ray powder diffraction（XRD） and electrorheological（ER） tests. Under an external electricfield, electrorheological properties of the suspension containing such Cr-doped and undoped Bi Fe O3 particles were investigated by steady shear experiments. It was found that the suspension of Cr-doped Bi Fe O3 particles possesses a better ER effect than that of pure Bi Fe O3 particles. Furthermore, different Cr-doped concentration plays an important role on the ER behavior. Combining the dielectric analysis, the enhanced ER effect of Cr-doped Bi Fe O3 suspension can be attributed to the improved interfacialpolarization.（2）Flower-like Fe₂O₃/polyaniline core/shell nanocomposite was obtained via a two-steps method. Firstly, monodispersed flower-like iron oxide was synthesized by a high temperature refluxing method. Then flower-like Fe2O3/polyaniline core/shell nanocomposite was further obtained via the in-situ polymerization. Scanning electron microscopy（SEM）, X-ray diffraction（XRD）, transmission electron microscopy（TEM）, SQUID MPMS, UV-vis and Haake rheometer were used to investigate its structure, morphology and properties. The obtained Fe2O3/polyaniline nanocomposite reveals an interesting morphological combination of hierarchical and core/shell structure. Its electrorheological（ER） behavior were investigated using a rotational rheometer under different applied electric field strengths when dispersed in silicone oil, which shown anobvious ER activity.（3） Anisotropic titanium oxide/polyaniline core/shell nanocomposite was synthesized via a three-step method, and its electrorheological（ER） properties under external applied electric field were researched. Firstly, monodispersed amorphous titanium oxide nanospheres were prepared by a controlled hydrolysis method, and then anisotropic titanium oxide nanospheres was obtained by using weak acid to etch monodispersed titanium oxide spheres. At last, the surface of anisotropic Ti O2 was coated with polyaniline（PANI） through an in-situ polymerization method. Then the influence factors on the preparation of anisotropic Ti O2/polyaniline core/shell structure nanoparticles were discussed deeply, including different kinds and amounts of acid, the amount of aniline, and so on. The morphology and structure of the samples were characterized by scanning electron microscopy, transmission electron microscopy, zeta potential analysis and X-ray powder diffraction, respectively. The electrorheological behaviors of the anisotropic Ti O2/polyaniline composite particles are characterized using a Haake rheometer, which shown a good ER activity.（4）Polyaniline/polypyrrole nano composite fibers with rough surface included two steps, the first one is the preparation of polyaniline fibers, and the second is the polypyrrole coating on polyaniline fiber. Because of the polymerization of aniline and pyrrole can be prepared by using the same initiator, so the whole experiment is simple. Then the influence factors on the preparation of polyaniline/ polypyrrole core/shell structure nanofibers were discussed deeply, including the amounts of pyrrole and different reaction time. The morphology and structure of the samples were characterized by scanning electron microscopy, transmission electron microscopy, UV visible spectroscopy and Fourier infrared spectrum analysis, respectively. The electrorheological behaviors of the polyaniline/polypyrrole composite particles are characterized using a Haake rheometer. At the same time, this chapter also discussed the pyrrole and the amount of pyrrole polymerization time on the influence of morphology and properties. By means of scanning electron microscopy, transmission electron microscopy, on the sample morphology and structure were characterized. Using a HAAKE rheometer test of polyaniline/polypyrrole composite particle electrorheological behavior.